In a UMTS (Universal Mobile Telecommunications System) network, long-term evolution (LTE) has been under study for the purposes of further increasing high-speed data rates, providing low delay and so on (non-patent literature 1). In LTE, as multiple access schemes, a scheme that is based on OFDMA (Orthogonal Frequency Division Multiple Access) is used on downlink channels (downlink), and a scheme that is based on SC-FDMA (Single Carrier Frequency Division Multiple Access) is used on uplink channels (uplink).
In the LTE system, uplink signals are mapped to adequate radio resources and transmitted from a mobile terminal apparatus to a radio base station apparatus. To be more specific, uplink user data is transmitted using an uplink shared channel (PUSCH: Physical Uplink Shared Channel). Also, uplink control information (UCI) is transmitted using the PUSCH when transmitted with uplink user data, and transmitted using an uplink control channel (PUCCH: Physical Uplink Control Channel) when transmitted alone.
The uplink control information (UCI) includes a delivery acknowledgment (ACK/NACK) in response to a downlink shared channel (PDSCH: Physical Downlink Shared Channel), a scheduling request, channel state information (CSI), and so on (see, for example, non-patent literature 2). The channel state information (hereinafter referred to as “CSI”) refers to information that is based on the instantaneous downlink channel state, and includes, for example, channel quality information (CQI), a precoding matrix indicator (PMI), a rank indicator (RI) and so on. This CSI is reported from a mobile terminal apparatus to a radio base station apparatus periodically or aperiodically.
Meanwhile, successor systems of LTE (referred to as, for example, “LTE-Advanced” or “LTE enhancement” (hereinafter referred to as “LTE-A”)) are under study for the purpose of achieving further broadbandization and increased speed beyond LTE. In LTE-A (Rel-10), high peak data rates are achieved by grouping a plurality of component carriers (CCs), where the system band of the LTE system is one unit, to provide a wide band (carrier aggregation). Also, an overlay network (HetNet: Heterogeneous Network) configuration to provide base stations of varying transmission power and various formats such as pico base stations, femto base stations and RRH (Remote Radio Head) base stations, in addition to conventional macro base stations, is under study. In 3GPP, time-domain interference coordination (eICIC: enhanced Inter-Cell Interference Coordination) has been standardized, as an interference coordination technique in a HetNet, to achieve further expansion of system capacity.